Section 5. Technology Characterization Microturbines

U.S. Environmental Protection Agency

Combined Heat and Power Partnership

March 2015

Section 5. Technology

Characterization –

Microturbines

Response and comments regarding: CALIFORNIA CODE OF REGULATIONS TITLE 3. FOOD AND AGRICULTURE DIVISION 8. MEDICAL CANNABIS CULTIVATION CHAPTER 1. MEDICAL CANNABIS CULTIVATION PROGRAM May 30, 2017

Attachment # 2 Combined Heat and Power

Acknowledgments

This Guide was prepared by Ken Darrow, Rick Tidball, James Wang and Anne Hampson at ICF

International, with funding from the U.S. Environmental Protection Agency and the U.S.

Department of Energy.

Catalog of CHP Technologies

Catalog of CHP Technologies 5–1 Microturbines

Section 5. Technology Characterization – Microturbines

5.1 Introduction

Microturbines, as the name implies, are small combustion turbines that burn gaseous or liquid fuels to

drive an electrical generator, and have been commercially available for more than a decade. Today’s

microturbine technology is the result of development work in small stationary and automotive gas

turbines, auxiliary power equipment, and turbochargers, much of which took place in the automotive

industry beginning in the 1950s. The development of microturbine systems was accelerated by the

similarity of design to large engine turbochargers, and that provided the basis for the engineering and

manufacturing technology of microturbine components.

During the 1990s several companies developed competing microturbine products and entered, or

planned to enter, the market. As the market matured, the industry underwent a consolidation phase

during which companies merged, changed hands, or dropped out of the market. In the United States

today, this has led to two main manufacturers of stationary microturbine products – Capstone Turbine

Corporation and FlexEnergy.

Table 5-1 provides a summary of microturbine attributes. Microturbines range in size from 30 to 330

kilowatts (kW). Integrated packages consisting of multiple microturbine generators are available up to

1,000 kW, and such multiple units are commonly installed at sites to achieve larger power outputs.

Microturbines are able to operate on a variety of fuels, including natural gas, sour gas (high sulfur, low

Btu content), and liquid petroleum fuels (e.g., gasoline, kerosene, diesel fuel, and heating oil).

Table 5-1. Summary of Microturbine Attributes

Electrical Output Available from 30 to 330 kW with integrated modular packages up to 1,000 kW.

Thermal Output Exhaust temperatures in the range of 500 to 600 °F, suitable for supplying a

variety of site thermal needs, including hot water, steam, and chilled water

(using an absorption chiller).

Fuel Flexibility Can utilize a number of different fuels, including natural gas, sour gas (high

sulfur, low Btu content), and liquid fuels (e.g., gasoline, kerosene, diesel fuel, and

heating oil).

Reliability and life Design life is estimated to be 40,000 to 80,000 hours with overhaul.

Emissions Low NOx combustion when operating on natural gas; capable of meeting

stringent California standards with carbon monoxide/volatile organic compound

(CO/VOC) oxidation catalyst.

Modularity Units may be connected in parallel to serve larger loads and to provide power

reliability.

Part-load Operation Units can be operated to follow load with some efficiency penalties.

Dimensions Compact and light weight, 2.3-2.7 cubic feet (cf) and 40-50 pounds per kW.

5.2 Applications

Microturbines are ideally suited for distributed generation applications due to their flexibility in

connection methods, their ability to be stacked in parallel to serve larger loads, their ability to provide


stable and reliable power, and their low emissions compared to reciprocating engines. Important

applications and functions are described below:

• Combined heat and power (CHP) – microturbines are well suited to be used in CHP applications

because the exhaust heat can either be recovered in a heat recovery boiler, or the hot exhaust

gases can be used directly. Typical natural gas fueled CHP markets include:

o Commercial – hotels, nursing homes, health clubs o Institutional – public buildings

o Industrial – small operations needing hot water or low pressure steam for wash water

as in the food and manufacturing sectors

• Combined cooling heating and power (CCHP) – The temperature available for microturbine

exhaust allows effective use with absorption cooling equipment that is driven either by low

pressure steam or by the exhaust heat directly. Cooling can be added to CHP in a variety of

commercial/institutional applications to provide both cooling and heating.

• Resource recovery – the ability of microturbines to burn a variety of fuels make it useful for

resource recovery applications including landfill gas, digester gas, oil and gas field pumping and

power applications, and coal mine methane use.

• Peak shaving and base load power (grid parallel).

• Thermal oxidation of very low Btu fuel or waste streams – Microturbine systems have been

designed to provide thermal oxidation for applications needing methane or volatile organic

compound destruction such as for landfill gas or other waste gases.

• Premium power and power quality – due to the inverter based generators, power quality

functionality can be added to CHP, and power-only applications allowing the system to be part

of an overall uninterruptible power supply (UPS) system providing black start capability and

back-up power capability to provide power when the electrical grid is down. The system can also

provide voltage and other power quality support. Such functions are useful for applications with

high outage costs and sensitive power needs including small data centers, hospitals, nursing

homes, and a variety of other applications that have critical service requirements.

• Power only applications – microturbines can be used for stand-alone power in remote

applications where grid power is either unavailable or very high cost. The systems can also run

as back-up power or in peak-shaving mode, though such use is limited.

• Microgrid – Microturbines are inverter based generation, and are therefore well-suited for

application in utility microgrids, providing grid support and grid communication functions. This

area of use is in a development and demonstration phase by electric power companies.


5.3 Technology Description

5.3.1 Basic Process

Microturbines operate on the same thermodynamic cycle (Brayton Cycle) as larger gas turbines and share

many of the same basic components. In this cycle, atmospheric air is compressed, heated (usually by

introducing and burning fuel), and then these hot gases drive an expansion turbine that drives both the

inlet compressor and a drive shaft capable of providing mechanical or electrical power. Other than the size

difference, microturbines differ from larger gas turbines in that they typically have lower compression

ratios and operate at lower combustion temperatures. In order to increase efficiency, microturbines

recover a portion of the exhaust heat in a heat exchanger called a recuperator, to increase the energy of

the gases entering the expansion turbine thereby boosting efficiency. Microturbines operate at high

rotational speeds of up to 60,000 revolutions per minute. Of the two primary players in the domestic

industry, Capstone couples this shaft output directly to a high speed generator and uses power electronics

to produce 60 Hz electricity. FlexEnergy uses a gearbox to reduce the drive speed to 3600 rpm to power a

synchronous electric generator.

5.3.2 Components

Figure 5-1 shows a schematic diagram of the basic microturbine components, which include the

combined compressor/turbine unit, generator, recuperator, combustor, and CHP heat exchanger. Each

of these primary components is described further below.

Figure 5-1. Microturbine-based CHP System Schematic

Source: FlexEnergy

5.3.2.1 Turbine & Compressor

The heart of the microturbine is the compressor-turbine package (or turbocompressor), which is

commonly mounted on a single shaft along with the electric generator. The shaft, rotating at upwards of

60,000 rpm, is supported on either air bearings or conventional lubricated bearings. The single moving

part of the one-shaft design has the potential for reducing maintenance needs and enhancing overall

reliability.


Microturbine turbomachinery is based on single-stage radial flow compressors and turbines, unlike

larger turbines that use multi-stage axial flow designs. Radial design turbomachinery handles the small

volumetric flows of air and combustion products with reasonably high component efficiency.84 Large-

1 With axial flow turbomachinery, blade height would be too small to be practical.

size axial flow turbines and compressors are typically more efficient than radial flow components.

However, in the size range for microturbines – 0.5 to 5 lbs/second of air/gas flow – radial flow

components offer minimum surface and end wall losses thereby improving efficiency.

As mentioned earlier, microturbines operate on either oil-lubricated or air bearings, which support the

shaft. Oil-lubricated bearings are mechanical bearings and come in three main forms – high-speed metal

roller, floating sleeve, and ceramic surface. Ceramic surface bearings typically offer the most attractive

benefits in terms of life, operating temperature, and lubricant flow. While they are a well-established

technology, they require an oil pump, oil filtering system, and liquid cooling that add to microturbine

cost and maintenance. In addition, the exhaust from machines featuring oil-lubricated bearings may not

be useable for direct space heating in cogeneration configurations due to the potential for air

contamination.

Air bearings allow the turbine to spin on a thin layer of air, so friction is low and rpm is high. They have

been in service on airplane cabin cooling systems for many years. No oil or oil pump is needed. Air

bearings offer simplicity of operation without the cost, reliability concerns, maintenance requirements,

or power drain of an oil supply and filtering system.

5.3.2.2 Generator

The microturbine produces electrical power either via a high-speed generator turning on the single

turbo-compressor shaft or through a speed reduction gearbox driving a conventional 3,600 rpm

generator. The high-speed generator single-shaft design employs a permanent magnet, and an aircooled

generator producing variable voltage and high-frequency AC power. This high frequency AC output

(about 1,600 Hz for a 30 kW machine) is converted to constant 60 Hz power output in a power

conditioning unit. Power conditioning involves rectifying the high frequency AC to DC, and then inverting

the DC to 60 Hz AC. However, power conversion comes with an efficiency penalty (approximately 5

percent). In addition to the digital power controllers converting the high frequency AC power into usable

electricity, they also filter to reduce harmonic distortion in the output. The power conditioning unit is a

critical component in the single-shaft microturbine design and represents significant design challenges,

specifically in matching turbine output to the required load. To accommodate transients and voltage

spikes, power electronic units are generally designed to handle seven times the nominal voltage. Most

microturbine power electronics generate three-phase electricity.

To start-up a single shaft design, the generator acts as a motor turning the turbo-compressor shaft until

sufficient rpm is reached to start the combustor. If the system is operating independent of the grid

(black starting), a power storage unit (typically a battery) is used to power the generator for start-up.

Electronic components also direct all of the operating and startup functions. Microturbines are generally

equipped with controls that allow the unit to be operated in parallel or independent of the grid, and


internally incorporate many of the grid and system protection features required for interconnection. The

controls also allow for remote monitoring and operation.

Figure 5-2 provides an example of the compact design of the basic microturbine components (in this

case, for the Capstone model C200 (200 kW)). The turbocompressor section, riding on air bearings,

drives the high speed, air cooled generator. The entire assembly is surrounded by a can-like structure

housing the recuperator and the combustion chamber.

Figure 5-2. Compact Microturbine Design

Source: Capstone Turbines, C200

5.3.2.3 Recuperator & Combustor

The recuperator is a heat exchanger that uses the hot turbine exhaust gas (typically around 1,200ºF) to

preheat the compressed air (typically around 300ºF) going into the combustor, thereby reducing the fuel

needed to heat the compressed air to the required turbine inlet temperature. Depending on

microturbine operating parameters, recuperators can more than double machine efficiency. However,

since there is increased pressure drop on both the compressed air and turbine exhaust sides of the

recuperator, this increased efficiency comes at the expense of about a 10-15 percent drop in power

output.

5.3.2.4 CHP Heat Exchanger

In CHP operation, microturbines offer an additional heat exchanger package, integrated with the basic

system, that extracts much of the remaining energy in the turbine exhaust, which exits the recuperator

at about 500-600o F. Exhaust heat can be used for a number of different applications, including potable

water heating, space heating, thermally activated cooling and dehumidification systems (absorption

chillers, desiccant dehumidification). Because microturbine exhaust is clean and has a high percentage

(15 percent) of oxygen, it can also be used directly for process applications such as driving a

doubleeffect absorption chiller or providing preheat combustion air for a boiler or process heat

application.


5.4 Performance Characteristics

Table 5-2 summarizes cost and performance characteristics for typical microturbine CHP systems

ranging in size from 30 kW to 1 MW. Heat rates and efficiencies are based on manufacturers’

specifications for systems operating on natural gas, the predominant fuel choice in CHP applications. The

table assumes that natural gas is delivered at typical low delivery pressures which require a booster

compressor to raise the gas pressure to the point at which it can be introduced into the compressed

inlet air-stream. Electrical efficiencies and heat rates shown are net of power losses from the gas

booster compressor. Customers that have, or can gain access to, high pressure gas from their local gas

utility can avoid the capacity and efficiency losses due to fuel gas compression. Capital costs, described

in more detail in a later section, are based on assumptions of a basic grid connect installation.

Installation costs can vary widely depending on site conditions and regional differences in material,

labor, and site costs. Available thermal energy is calculated based on manufacturer specifications on

turbine exhaust flows and temperatures. CHP thermal recovery estimates are based on producing hot

water for process or space heating applications. All performance specifications are at full load

International Organization for Standards (ISO) conditions (59 oF, 60 percent RH, 14.7 psia).

The data in the table show that electrical efficiency generally increases as the microturbine becomes

larger. Microturbines have lower electrical efficiencies than reciprocating engines and fuel cells, but are

capable of high overall CHP efficiencies. The low power to heat ratios (P/H) of microturbines (which

implies relatively more heat production), makes it important for both overall efficiency and for

economics to be sited and sized for applications that allow full utilization of the available thermal

energy.

As shown, microturbines typically require 50 to 140 psig fuel supply pressure. Local distribution gas

pressures usually range from 30 to 130 psig in feeder lines and from 1 to 50 psig in final distribution

lines. If available, sites that install microturbines will generally opt for high pressure gas delivery rather

than adding the cost of a booster compressor with its accompanying efficiency and capacity losses.

Estimated installed capital costs range from $4,300/kW for the 30 kW system down to $2,500/kW for

the 1,000 kW system – described in more detail in Section Capital Cost.

Table 5-2. Microturbine Cost and Performance Characteristics

Microturbine Characteristics [1] System

1 2 3 4 5 6

Nominal Electricity Capacity (kW) 30 65 200 250 333 1000

Compressor Parasitic Power (kW) 2 4 10 10 13 50

Net Electricity Capacity (kW) 28 61 190 240 320 950

Fuel Input (MMBtu/hr), HHV 0.434 0.876 2.431 3.139 3.894 12.155

Required Fuel Gas Pressure (psig) 55-60 75-80 75-80 80-140 90-140 75-80

Electric Heat Rate (Btu/kWh), LHV [2] 13,995 12,966 11,553 11,809 10,987 11,553

Electric Efficiency (%), LHV [3] 24.4% 26.3% 29.5% 28.9% 31.1% 29.5%


Electric Heat Rate (Btu/kWh), HHV 15,535 14,393 12,824 13,110 12,198 12,824

Electric Efficiency (%), HHV 21.9% 23.7% 26.6% 26.0% 28.0% 26.6%

CHP Characteristics

Exhaust Flow (lbs/sec) 0.68 1.13 2.93 4.7 5.3 14.7

Exhaust Temp (oF) 530 592 535 493 512 535

Heat Exchanger Exhaust Temp (oF) 190 190 200 190 190 200

Heat Output (MMBtu/hr) 0.21 0.41 0.88 1.28 1.54 4.43

Table 5-2. Microturbine Cost and Performance Characteristics

Microturbine Characteristics [1] System

1 2 3 4 5 6

Heat Output (kW equivalent) 61.0 119.8 258.9 375.6 450.2 1,299.0

Total CHP Efficiency (%), HHV [4] 70.0% 70.4% 63.0% 66.9% 67.5% 63.1%

Total CHP Efficiency (%), LHV 77.3% 77.8% 69.6% 73.9% 74.6% 69.8%

Power/Heat Ratio [5] 0.46 0.51 0.73 0.64 0.71 0.73

Net Heat Rate (Btu/kWh) [6] 6,211 5,983 6,983 6,405 6,170 6,963

Effective Electric Eff. (%), HHV [7] 54.9% 57.0% 48.9% 53.3% 55.3% 49.0%

Cost

CHP Package Cost ($/kW) [8] $2,690 $2,120 $2,120 $1,840 $1,770 $1,710

Total Installed Cost ($/kW) [9] $4,300 $3,220 $3,150 $2,720 $2,580 $2,500

Notes: 1. Characteristics presented are representative of commercially available microturbine systems. Table data are based from

smallest to largest: Capstone C30,; Capstone C65 CARB, Capstone C200 CARB, FlexEnergy MT250, FlexEnergy MT330,

Capstone C1000-LE 2. Turbine and engine manufacturers quote heat rates in terms of the lower heating value (LHV) of the fuel. Gas utilities

typically report the energy content on a higher heating value (HHV) basis. In addition, electric utilities measure power plant

heat rates in terms of HHV. For natural gas, the average heat content is near 1,030 Btu/scf on an HHV basis and about 930

Btu/scf on an LHV basis – a ratio of approximately 0.9 (LHV / HHV). 3. Electrical efficiencies are net of parasitic and conversion losses. Fuel gas compressor needs based on 1 psi inlet supply. 4. Total Efficiency = (net electricity generated + net heat produced for thermal needs)/total system fuel input 5. Power/Heat Ratio = CHP electrical power output (Btu)/ useful heat output (Btu) 6. Net Heat Rate = (total fuel input to the CHP system - the fuel that would be normally used to generate the same amount of

thermal output as the CHP system output assuming an efficiency of 80 percent)/CHP electric output (kW). 7. Effective Electrical Efficiency = (CHP electric power output) / (total fuel into CHP system – total heat recovered/0.8). 8. Equipment cost only. The cost for all units, except the 30 kW size, includes integral heat recovery water heater. All units

include a fuel gas booster compressor. 9. Installed costs based on CHP system producing hot water from exhaust heat recovery in a basic installation in grid connect

mode.


5.4.1 Part-Load Performance

Microturbines that are in applications that require electric load following must operate during some

periods at part load. Although, operationally, most installations are designed to operate at a constant

output without load-following or frequent starts and stops. Multiple unit installations can achieve load

following through sequentially turning on more units requiring less need for part load operation. When

less than full electrical power is required from a microturbine, the output is reduced by a combination of

mass flow reduction (achieved by decreasing the compressor speed) and turbine inlet temperature

reduction. In addition to reducing power, this change in operating conditions also reduces efficiency.

Figure 5-3 shows a sample part-load efficiency curve for the Capstone C65. At 50 percent power output,

the electrical efficiency drops by about 15 percent (decline from approximately 30 percent to 25

percent). However, at 50 percent power output, the thermal output of the unit only drops 41 percent

resulting in a net loss of CHP efficiency of only 5 percent.

Figure 5-3. Part Load Efficiency at ISO Conditions, Capstone C65

Source: Capstone, C65 Technical Reference

5.4.2 Effects of Ambient Conditions on Performance

The ambient conditions (temperature and air pressure) under which a microturbine operates have a

noticeable effect on both the power output and efficiency. This section provides a better understanding

of the changes observed due to changes in temperature and air pressure. At elevated inlet air

temperatures, both the power and efficiency decrease. The power decreases due to the decreased mass

flow rate of air (since the density of air declines as temperature increases), and the efficiency decreases

because the compressor requires more power to compress air that is less dense. Conversely, the power

and efficiency increase with reduced inlet air temperature.


Figure 5-5 shows the variation in power and efficiency for a microturbine as a function of ambient

temperature compared to the reference International Organization for Standards (ISO) condition of sea

level and 59°F. The density of air decreases at altitudes above sea level. Consequently, power output

decreases. Figure 5-4 shows the effect of temperature on output, and Figure 5-5 shows the effect on

efficiency for the Capstone C200. The Capstone unit maintains a steady output up to 70-80 oF due to a

limit on the generator output. However, the efficiency declines more uniformly as ambient temperature

increases. Figure 5-6 shows a combined power and efficiency curve for the FlexEnergy MT250. For this

model, both power output and efficiency change more or less uniformly above and below the ISO rating

point.

Figure 5-4. Temperature Effect on Power, Capstone C200-LP

Source: Capstone Turbines


Figure 5-5. Temperature Effect on Efficiency, Capstone C200-LP


Figure 5-6. Temperature Effect on Power and Efficiency, FlexEnergy MT250

Source: FlexEnergy


Inlet air cooling can mitigate the decreased power and efficiency resulting from high ambient air

temperatures. While inlet air cooling is not a feature on today’s microturbines, cooling techniques now

entering the market, or being employed, on large gas turbines may work their way into next generation

microturbine products.

Evaporative cooling, a relatively low capital cost technique, is the most likely inlet air cooling technology

to be applied to microturbines. It uses a very fine spray of water directly into the inlet air stream.

Evaporation of the water reduces the temperature of the air. Since cooling is limited to the wet bulb air

temperature, evaporative cooling is most effective when the wet bulb temperature is significantly below

the dry bulb temperature. In most locales with high daytime dry bulb temperatures, the wet bulb

temperature is often 20ºF lower. This temperature difference affords an opportunity for substantial

evaporative cooling. However, evaporative cooling can consume large quantities of water, making it

difficult to operate in arid climates.

Refrigeration cooling in microturbines is also technically feasible. In refrigeration cooling, a

compressiondriven or thermally activated (absorption) refrigeration cycle cools the inlet air through a

heat exchanger. The heat exchanger in the inlet air stream causes an additional pressure drop in the air

entering the compressor, thereby slightly lowering cycle power and efficiency. However, as the inlet air

is now substantially cooler than the ambient air, there is a significant net gain in power and efficiency.

Electric motor driven refrigeration results in a substantial amount of parasitic power loss. Thermally

activated absorption cooling can use waste heat from the microturbine, reducing the direct parasitic

loss. The relative complexity and cost of these approaches, in comparison with evaporative cooling,

render them less likely.

Finally, it is also technically feasible to use thermal energy storage systems – typically ice, chilled water,

or low-temperature fluids – to cool inlet air. These systems eliminate most parasitic losses from the

augmented power capacity. Thermal energy storage is a viable option if on-peak power pricing only

occurs a few hours a day. In that case, the shorter time of energy storage discharge and longer time for

daily charging allow for a smaller and less expensive thermal energy storage system.

The density of air also decreases with increasing altitude. The effect of altitude derating on the Capstone

C65 is shown in Figure 5-7. An installation in the mile high city of Denver would have a capacity of only

56 kW – a 14 percent drop in capacity. Unlike the effects of temperature rise, an increase in altitude at a

given temperature does not have much impact on energy efficiency. The units operate at nearly the

same efficiency, though at a lower output.


Figure 5-7. Ambient Elevation vs. Temperature Derating, Capstone C65


Gas turbine and microturbine performance is also affected by inlet and exhaust back-pressure. ISO

ratings are at zero inlet pressure with no exhaust back-pressure. Adding the additional CHP heat

exchanger definitely produces some increase in exhaust back pressure. Pressure drops on the inlet side

from air filters also reduces the system output and efficiency. For the C65 shown in the previous figure,

every 1” pressure drop on the inlet side produces roughly a 0.6 percent drop in power and a 0.2 percent

drop in efficiency. A 1” pressure drop on the exhaust side produces about a 0.35 percent drop in power

and a 0.25 percent drop in efficiency.

It is important when evaluating microturbine performance at a given site to consider all of the derating

factors that are relevant: site altitude, average temperature and seasonal temperature swings, and

pressure loss derating resulting from filters and the CHP heat recovery system. The combination of these

factors can have a significant impact on both capacity and efficiency. Reduction in capacity also impacts

the unit costs of the equipment because the same costs are being spread over fewer kilowatts.

5.4.3 Capital Cost

This section provides study estimates of capital costs for basic microturbine CHP installations. It is

assumed that the thermal energy extracted from the microturbine exhaust is used for producing hot

water for use on-site. Equipment-only and installed costs are estimated for each representative

microturbine system. It should be emphasized that installed costs can vary significantly depending on

the scope of the plant equipment, geographical area, competitive market conditions, special site


requirements, emissions control requirements, prevailing labor rates, and whether the system is a new

or a retrofit application.

Table 5-3 provides cost estimates for combined heat and power applications, assuming that the CHP

system produces hot water and that there is no fuel pretreatment. Thermal recovery in the form of

cooling can be accomplished with the addition of an absorption chiller – not included in this comparison.

The basic microturbine package consists of the microturbine and power electronics. All of the

commercial and near-commercial units offer basic interconnection and paralleling functionality as part

of the package cost. All but one of the systems offers an integrated heat exchanger heat recovery

system for CHP within the package.

There is little additional equipment that is required for these integrated systems. A heat recovery system

has been added where needed, and additional controls and remote monitoring equipment have been

added. The total plant cost consists of total equipment cost plus installation labor and materials

(including site work), engineering, project management (including licensing, insurance, commissioning

and startup), and financial carrying costs during a typical 3-month construction period.

The basic equipment costs represent material on the loading dock, ready to ship. It includes the cost of

the generator package, the heat recovery, the flue gas compression and interconnection equipment

cost. As shown in the table, the cost to a customer for installing a microturbine-based CHP system

includes a number of other factors that increase the total costs by 70-80 percent.

Labor/materials represent the labor cost for the civil, mechanical, and electrical work and materials such

as ductwork, piping, and wiring. A number of other costs are also incurred. These costs are often

referred to as soft costs and they vary widely by installation, by development channel and by approach

to project management. Engineering costs are required to design the system and integrate it

functionally with the application’s electrical and mechanical systems. In this characterization,

environmental permitting fees are included. Project and construction management also includes general

contractor markup, and bonding and performance guarantees. Contingency is assumed to be 5 percent

of the total equipment cost in all cases. An estimated financial interest of 5 percent during a 3-month

construction period is also included.

The cost estimates shown represent a basic installation. In the California Self-Generation incentive

Program (SGIP) the average installation cost for 116 non-renewable fuel microturbine systems between

2001-2008 was $3,150/kW. For 26 renewable fueled systems over the same time period, the average

installed cost was $3,970/kW.1

Table 5-3. Equipment and Installation Costs

System

1 2 3 4 5 6

Electric Capacity

Nominal Capacity (kW) 30 65 200 250 333 1000

1 CPUC Self-Generation Incentive Program: Cost Effectiveness of Distributed Generation Technologies, ITRON, Inc., 2011.


Net Capacity (kW) 28 61 190 240 320 950

Table 5-3. Equipment and Installation Costs

System

1 2 3 4 5 6

Equipment Costs

Gen Set Package $53,100 $112,900 $359,300 $441,200 $566,400 $1,188,600

Heat Recovery $13,500 $0 $0 $0 $0 $275,000

Fuel Gas Compression $8,700 $16,400 $42,600 $0 $0 $164,000

Interconnection $0 $0 $0 $0 $0 $0

Total Equipment ($) $75,300 $129,300 $401,900 $441,200 $566,400 $1,627,600

($/kW) $2,689 $2,120 $2,120 $1,840 $1,770 $1,710

Installation Costs

Labor/Materials $22,600 $28,400 $80,400 $83,800 $101,900 $293,000

Project & Construction Mgmt $9,000 $15,500 $48,200 $52,900 $68,000 $195,300

Engineering and Fees $9,000 $15,500 $44,200 $48,500 $56,600 $162,800

Project Contingency $3,800 $6,500 $20,100 $22,100 $28,300 $81,400

Financing (int. during const.) $700 $1,200 $3,700 $4,100 $5,100 $14,800

Total Other Costs ($) $45,100 $67,100 $196,600 $211,400 $259,900 $747,300

($/kW) $1,611 $1,100 $1,035 $881 $812 $787

Total Installed Cost ($) $120,400 $196,400 $598,500 $652,600 $826,300 $2,374,900

($/kW) $4,300 $3,220 $3,150 $2,720 $2,580 $2,500

Source: Microturbine package costs and equipment from the vendors; installation costs developed by ICF.

As the table shows, there are economies of scale as sizes get larger. From 30 to 333 kW capital costs

increase as the 0.8 power factor of the capacity increase2 – a 100 percent increase in size results in an 80

percent increase in capital cost. Similar scale economies also exist for multiple unit installations such as

the 1,000 kW unit comprised of five 200-kW units. The unit cost of the larger system is only 80 percent

of the cost of the single unit.

2 0.8

(Cost1/Cost2) = (Size1/Size2)


5.4.4 Maintenance

Maintenance costs vary with size, fuel type and technology (air versus oil bearings). A typical

maintenance schedule is shown in Table 5-4.

Table 5-4. Example Service Schedule, Capstone C65

Maintenance Interval

Component Maintenance

Action Comments

24 months UCB Battery Replace ---

4,000 hours Engine Air Filter Inspect Replace if application requires

Electronics Air Filter Inspect Clean if necessary

Fuel Filter Element (external) Inspect Replace if application requires (not

required for gas pack)

Table 5-4. Example Service Schedule, Capstone C65

Maintenance Interval

Component Maintenance

Action Comments

Fuel System Leak Check ---

8,000 hours Engine Air Filter Replace ---

Electronics Air Filter Clean ---

Fuel Filter Element (external) Replace Not required for gas pack

Igniter Replace ---

ICHP Actuator Replace ---

20,000 hours

or 3 years Battery Pack Replace ---

20,000 hours Injector Assemblies Replace ---

TET Thermocouple Replace ---

SPV Replace Replace with Woodward valve upgrade

kit

40,000 hours Electronic Components: ECM, LCM, & BCM Power Boards, BCM & ECM Fan Filters, Fans, EMI Filter, Frame PM

Replace Kits available for each major

configuration

Engine Replace Remanufactured or new

Source: Adapted from Capstone C65 User’s Manual.

Most manufacturers offer service contracts that cover scheduled and unscheduled events. The cost of a

full service contract covers the inspections and component replacements outlined in Table 5-5, including

replacement or rebuild of the main turbocompressor engine components. Full service costs vary

according to fuel type and service as shown.


Table 5-5. Maintenance Costs Based on Factory Service Contracts

Maintenance Costs System

1 2 3 4 5 6

Nominal Electricity Capacity

(kW) 30 65 200 250 333 1000

Fixed ($/kW/yr) --- --- --- $9.120 $6.847 ---

Variable ($/kWh) --- --- --- $0.010 $0.007 ---

Average @ 6,000 hrs/year

operation ($/kWh) --- $0.013 $0.016 $0.011 $0.009 $0.012

Source: Compiled by ICF from vendor supplied data

Maintenance requirements can be affected by fuel type and site conditions. Waste gas and liquid fuel

applications may require more frequent inspections and component replacement than natural gas

systems. Microturbines operating in dusty and/or dirty environments require more frequent inspections

and filter replacements.

5.4.5 Fuels

Stationary microturbines have been designed to use natural gas as their primary fuel. Microturbines

designed for transportation applications typically utilize a liquid fuel such as methanol. As previously

noted, microturbines are capable of operating on a variety of fuels including:

• Liquefied petroleum gas (LPG) – propane and butane mixtures

• Sour gas – unprocessed natural gas as it comes directly from a gas well

• Biogas – any of the combustible gases produced from biological degradation of organic wastes,

such as landfill gas, sewage digester gas, and animal waste digester gas

• Industrial waste gases – flare gases and process off-gases from refineries, chemical plants and

steel mills

• Manufactured gases – typically low- and medium-Btu gas produced as products of gasification

or pyrolysis processes

Some of the elements work as contaminants and are a concern with some waste fuels, specifically the

acid gas components (H2S, halogen acids, HCN, ammonia, salts and metal-containing compounds,

halogens, nitrogen compounds, and silicon compounds) and oils. In combustion, halogen and sulfur

compounds form halogen acids, SO2, some SO3, and possibly H2SO4 emissions. The acids can also corrode

downstream equipment. Solid particulates must be kept to low concentrations to prevent corrosion and

erosion of components. Various fuel scrubbing, droplet separation, and filtration steps are required if

fuel contaminant levels exceed manufacturer specifications. Landfill gas in particular often contains

chlorine compounds, sulfur compounds, organic acids, and silicon compounds which dictate fuel

pretreatment. A particular concern with wastewater treatment and landfill applications is the control of

siloxane compounds. Siloxanes are a prevalent manmade organic compound used in a variety of

products, and they eventually find their way into landfills and waste water. When siloxanes are exposed

to high temperatures inside the combustion and exhaust sections of the turbine, they form hard silicon

dioxide deposits that can eventually lead to turbine failure.


5.4.6 System Availability

Microturbine systems in the field have generally shown a high level of availability.3 The basic design and

low number of moving parts is conducive to high availability; manufacturers have targeted availabilities

of 98-99 percent. The use of multiple units or backup units at a site can further increase the availability

of the overall facility.

5.5 Emissions

Microturbines are designed to meet State and federal emissions regulations including more stringent

State emissions requirements such as in California and other states (e.g., the Northeast). All

microturbines operating on gaseous fuels feature lean premixed (dry low NOx, or DLN) combustor

technology. All of the example commercial units have been certified to meet extremely stringent

standards in Southern California of less than 4-5 ppmvd of NOx (15 percent O2.) After employing a

CO/VOC oxidation catalyst, carbon monoxide (CO) and volatile organic compound (VOC) emissions are at

the same level. “Non-California” versions have NOx emissions of less than 9 ppmvd. The emissions

characteristics are shown in Table 5-6.

Table 5-6. Microturbine Emissions Characteristics

System

1 2 3 4 5 6

Nominal Electric Capacity (kW) 30 65 200 240 320 1,000

Recovered Thermal Energy (kW) 61.0 119.8 258.9 376 450 1,299.0

Nominal Electrical Efficiency, HHV 23.6% 25.3% 28.1% 27.2% 29.2% 28.1%

NOx (ppm @ 15% O2, dry) [1] 9 4 4 5 9 4

NOx (lb/MWh) [2] 0.49 0.17 0.14 0.23 0.39 0.14

NOx (lb/MWh with CARB CHP credit) 0.16 0.06 0.06 0.09 0.16 0.06

CO (ppm @ 15% O2, dry) [1] 40 8 8 5 10 8

CO (lb/MWh) [3] 1.8 0.24 0.2 0.14 0.26 0.2

CO (lb/MWh with CARB CHP credit) 0.59 0.08 0.09 0.06 0.11 0.09

VOC (ppm @ 15% O2, dry) [1, 4] 9 3 3 5 9 3

VOC (lb/MWh) [5] 0.23 0.05 0.2 0.08 0.13 0.2

VOC (lb/MWh with CARB CHP credit) 0.08 0.02 0.09 0.03 0.06 0.09

CO2 (lb/MWh electric only) [6] 1,814 1,680 1,497 1,530 1,424 1,497

CO2 (lb/MWh with CARB CHP credit) 727 700 817 749 722 815

Notes:

3 Availability refers to the percentage of time that the system is either operating or available to operate. Conversely, the system

is unavailable when it is shut down for maintenance or when there has been a forced outage.


1. Vendor estimates for low emission models using natural gas fuel. For systems 1, 2, 3, and 6 the vendor

provided both input- (ppmv) and output-based emissions (lb/MWh.) For units 4 and 5, the output emissions

were calculated as described below.

2. Output based NOx emissions (lb/MWh) = (ppm @15% O2) X 3.413) / ((272 X (% efficiency HHV))

3. Output based CO emissions (lb/MWh) = (ppm @15% O2) X 3.413) / ((446 X (% efficiency HHV)) 4. Volatile organic compounds. 5. Output based VOC emissions (lb/MWh) = (ppm @15% O2) X 3.413) / ((782 X (% efficiency HHV)) 6. Based on 116.39 lbs CO2 / MMBtu.

The CO2 emissions estimates with CHP show the potential of microturbines in CHP applications to reduce

the emissions of CO2. Coal fired generation emits about 2,000 lb/MWh, and even state of the art natural

gas combined cycle power plants produce CO2 emissions in the 800-900 lb/MWh range, even before

transmission line losses are considered.

5.6 Future Developments

Microturbines first entered the market in the 30-75 kW size range. Of the last several years,

microturbine manufacturers have developed larger capacity products to achieve better economics of

operation through higher efficiencies and lower capital and maintenance costs.

Manufacturers are continuing to develop products with higher electrical efficiencies. Known

developments include a model Capstone is developing, with the Department of Energy, on a 250 kW

model with a target efficiency of 35 percent (gross output, LHV) and a 370 kW model with a projected 42

percent efficiency. The C250 is intended to feature an advanced aerodynamic compressor design, engine

sealing improvements, improved generator design with longer life magnet, and enhanced cooling.

Key technical developments of the C370 model, shown schematically in Figure 5-8, include:

• Dual property, high-temperature turbine

• High-pressure compressors (11:1) and recuperator

• Dual generators – both low pressure and high-pressure spool

• Dual spool control development

• High-temperature, low emissions combustor

• Inter-state compressor cooling


Figure 5-8. Capstone C370 Two-shaft High Efficiency Turbine Design

Source: DOE, Energy Efficiency and Renewable Energy Fact Sheet

The C370 model will use a modified Capstone C200 turbocompressor assembly as the low-pressure

section of a two shaft turbine. This low-pressure section will have an electrical output of 250 kW. A new

high-temperature, high-pressure turbocompressor assembly will increase the electrical output to 370

kW.

Section 5. Technology Characterization Microturbines

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